The presently-disclosed subject matter relates to the production of titanium dioxide (TiO2) nanowires, catalyst compositions and methods for desulfurization. In particular, the presently-disclosed subject matter relates to catalyst compositions and methods for desulfurization that make use of titanium(IV) oxide nanowires that include catalytically-active metal sulfide nano-particles or nanowires as an active phase, and more particularly wherein the metal is selected from the group consisting of molybdenum, nickel, cobalt, tungsten and a combination thereof.
Although the motor fuels market in the US is dominated by gasoline, the demand for diesel fuel remains strong and is growing. Comparing US demand in June 2014 to that of June 2015, clean-diesel vehicle sales increased by 25%, and demand for on-road diesel fuel increased by 11.8%. In contrast, demand for gasoline decreased by 3.4%. The market share for diesel-fueled vehicles, approximately 3% of US vehicle sales now, may double by 2018. Unfortunately, sulfur contamination is a major problem in diesel fuels.
Sulfur is a natural component in crude oil and therefore is also present in gasoline and diesel fuel. With respect to diesel, light cycle oil (LCO), a middle distillate product in the fluid catalytic cracking (FCC) of heavy oils, such as vacuum gas oil and atmospheric residue, is usually blended in the diesel pool. However, LCO, which comprises about 15% of the total US distillate pool, is a poor diesel fuel blending component, due to its low cetane number which is typically from about 15 to about 25, and its high sulfur content, which can range from about 2000 ppm to about 7000 ppm. The high sulfur content means that deep hydrotreatment is required to obtain sulfur-free and high-cetane-number fuel. In addition, the presence of sulfur increases SOx emissions, contributes to the emission of fine particulates, leads to the corrosion of engine systems (which decreases engine life), and irreversibly poisons the noble metal catalysts in the engine's converter. For all of these reasons, the reduction of sulfur in diesel fuel is important.
Since September 2007, all of the on-highway diesel fuel sold at gas stations in the United States is ultra-low-sulfur diesel (ULSD), for which the allowable sulfur content is 15 ppm. Beginning in 2017, new vehicle emission standards issued by the US EPA Tier 3 program will lower the allowable sulfur content of gasoline from 30 ppm to 10 ppm. Consequently, refineries are facing major challenges to meet this fuel sulfur specification.
Thus, in the past decade, clean fuels research, including ultra-deep desulfurization, has become a more important subject of environmental catalysis studies worldwide. One aspect of this research is identifying catalysts that can be highly effective in the hydrodesulfurization process (HDS). Related to this is identifying processes that can be highly efficient in producing catalysts for use in HDS processes.